Radiation sensitive apparatus for activating a fire or explosion protection system



May 19, 1970 c MCALISTER ETAL 3,513,311

RADIATION SENSITIVE APPARATUS FOR ACTIVATING A FIRE OR EXPLOSION PROTECTION SYSTEM Filed.F'eb. 29, 1968 18 14 l6 46 H 17 Q 2? 24 Quench One 44 (f/'Cuif /10 1 v02 /00' L +V +V M ill i U T I l8 IOU/JG One 54 Urea/Zr] S/IOT la. n N I 72 Pu/se One firm/try S hof 55 I051 [I U LUU 20b 68 I I 2% Pu/Je One Pulse One I Okay/if y Shof Fig.2.

INVENTORS. Charles 0. Mc A/isfer James R. Arr/mg for? ATTOR. i s.

United States Patent RADIATION SENSITIVE APPARATUS FOR ACTI- VATING A FIRE 0R EXPLOSION PROTECTION SYSTEM Charles D. McAlister, Blue Springs, Mo., and James R. Arrington, Muskego, Wis., assignors to Fike Metal Products Corporation, Blue Springs, Mo., a corporation of Missouri Filed Feb. 29, 1968, Ser. No. 709,428 Int. Cl. G01 /30 US. Cl. 25083.3 Claims ABSTRACT OF THE DISCLOSURE Dual channel ultraviolet radiation sensing by ionization discharge tubes is employed to activate a fire or explosion protection system. In one embodiment each channel is separately integrated and then fed to a respective input of an AND gate. One integrator responds to the maximum expected background radiation level and energizes a warning light, while the other integrator responds only to a higher radiation level indicative of a danger condition. In a second embodiment the channels are first fed to an AND gate, the output of the gate being delivered to a single integrator. In either arrangement the dual sensing tubes minimize the possibility of simultaneous exposure to stray radiation to permit high speed operation of the apparatus Without the hazard of inadvertent activation. A single channel version with dual integrators as above is also disclosed.

Various means have been employed to activate a sprinkler system or other protective venting or quenching system for fire control purposes. Ultraviolet sensors for the detection of flame are available and in use, but such sensors suffer from the disadvantage that they also respond to background radiation and are subject to random firing. Therefore, although highly efiicient in the rapid sensing of the presence of a flame, prior detection apparatus employing an ultraviolet sensor oftentimes has a delay in response time of from one to several seconds in order to prevent false activation of the fire control system by stray radiation. Commonly, the coil of an electromechanical relay is connected in series with the ultraviolet sensor, the relay being selected to have a pullin time and suflicient armature inertia to preclude operation of the relay contacts unless the sensor fires continuously for a period of approximately one second or more. In this manner, it is assured that a continuous ultraviolet source has been sensed before activation of the fire control system is effected.

Although there are some applications where activation apparatus of the above type is satisfactory, in many instances, such as in warehouse or laboratory areas, a response time of one or more seconds is sufficient to permit highly flammable substances to burn out of control before the sprinkler system is activated. Manifestly, this is particularly the case in applications Where a fire may be fed by explosive substances or generated within an eX plosive atmosphere.

It is, therefore, the primary object of this invention to provide a monitor of flame produced radiation which is capable of responding to such radiation in much less than a second and activating a suitable protective system.

As a corollary to the foregoing object it is an important aim of the instant invention to provide apparatus as aforesaid which will respond at high speed but is nonresponsive to stray radiation or high background radiation levels, thereby precluding false activation of the protective system.

Furthermore, it is an important object of the invention ice to provide apparatus as aforesaid which will deliver a warning when the intensity of the background radiation reaches a predetermined, maximum level indicative of a slowly developing danger condition or, alternatively, indicative of component failure within the apparatus or the necessity for readjustment thereof.

In the drawing:

FIG. 1 is a schematic and block diagram of one embodiment of the invention;

FIG. 2 is a partial schematic and block diagram showing a modified form of the embodiment of FIG. 1;

FIG. 3 is a schematic and block diagram of a second embodiment of the instant invention;

FIG. 4 is a graph illustrating the operation of one of the integrators; and

FIG. 5 is an electrical schematic diagram illustrating the quenching circuit in detail.

Referring to FIG. 1, radiation responsive pulse producing circuitry 10 is diagrammatically illustrated and comprises an ultraviolet sensitive photo-diode 11 having a cathode connection 12 and an anode connection 14 extending to a quenching circuit 16. The output of quenching circuit 16 is delivered to the input of a monostable multivibrator or one shot 18. A series connected diode 2(3, variable resistor 22, and fixed resistor 24 are connected between the output of one shot 18 and the inverting input of an integrated circuit operational amplifier 26, the latter being connected as an integrator. A current limiting resistor 28 and an integrating capacitor 30 are connected in series between the output of amplifier 26 and the inverting input thereof, a discharging diode 32 for shorting the capacitor 30 in one polarity direction being connected from the junction of resistor 28 and capacitor 30 to ground, as indicated by the symbol. In the various figures, the ground symbol denotes the common return for the negative side of the direct current supply potential. It should be understood that, of course, discrete solid state components may be employed if desired rather than the integrated circuit amplifier 26 to perform the various functions, including integration, to be discussed below.

A rapid saturation feedback diode 34 and a feedback capacitor 36 are connected in series between the output of amplifier 26 and the non-inverting input thereof, a resistor 38 being connected from the non-inverting input to ground. A positive bias for the inverting input of amplifier 26 is supplied through a resistor 40. Throughout the figures, the terminals designated +V represent the positive side of the low voltage, direct potential utilized for the operation of the integrated circuitry and other transistor components.

The output from amplifier 26 is in the form of a command signal delivered to one input of a two input AND gate 42, the output of AND gate 42 being connected to the gate terminal of a silicon controlled rectifier 44. The cathode-anode circuit of SCR 44 is connected in series with an electrically operated deluge valve 46, or other suitable electrically activated means for initiating the operation of a protective quenching or venting system for fire control. Positive high voltage is applied to supply terminal 48, the SCR 44 thus operating as a switch connected directly in the power circuit to the valve 46 or other electrical activator. In the use of the instant invention to discharge a suitable suppressant directly onto the fire or into the region containing the fire, the valve 46 may be of the explosively operated type shown and described in US. Letters Patent 3,363,801, owned by the assignee herein. In this regard, deluge valves activated by detonation open in appreciably less than one millisecond and thus are quite suitable for use with the instant invention.

The foregoing description was primarily directed to one of two radiation sensing and detecting channels of the embodiment of FIG. 1, the second channel being identical in structure to the first channel and including pulse producing circuitry a which delivers its output to a one shot 18a. It may be seen that the remainder of the components of the second channel through the output of operational amplifier 26a are identical to that as described above, such components being designated by the same reference numerals as above with the addition of a notation. The amplifier 26a delivers its output in the form of a command signal to the second input of AND gate 42. Thus, time coincidence of both command signals from the outputs of the amplifiers 26 and 26a is required in order to effect firing of the SCR 44.

An NPN switching transistor 50 controls the energization of a warning lamp 52, the latter being connected in series with an emitter resistor 54 for the transistor 50. The base of transistor 50 is connected to the output of amplifier 26 through an input resistor 56; the collector of transistor 50 is connected to the positive supply.

In FIG. 2, a modified, single channel form of the apparatus is illustrated. The FIG. 2 version is the same as the basic embodiment of FIG. 1 except that only the pulse producing circuitry 10 and the one shot 18 are utilized to provide a single input channel, the output of the one shot 18 being delivered to both of the diodes and 20a. Therefore, the input channel is split and directed to the inverting inputs of the two amplifiers 26 and 26a. The remainder of the apparatus is identical to that shown and described above with respect to the embodiment of FIG. 1; therefore, FIG. 2 is a fragmentary showing only.

A second embodiment of the invention is illustrated in FIG. 3 Where it may be seen that a dual channel input comprising pulse producing circuitries 10 and 10a and one shots 18 and 18a is employed. However, unlike the embodiment of FIG. 1, the outputs of the two one shots 18 and 1811 are fed to respective inputs of a two input AND gate 58. An operational amplifier 26b and associated components identical in structure to amplifiers 26 and 26a discussed and described above is utilized, with the exception that a resistor 65 is substituted for capacitor 36 in the feedback loop. Corresponding reference numerals are used for the components identical to those previously described, with the addition of the b.

The diode 20b is connected to the output of the AND gate 58, and the bias resistor 40b is connected to a voltage divider comprising series connector resistors 60 and 62, the resistor 60 being connected to the positive supply and having a normally open, pushbutton reset switch 64 connected in parallel therewith. The command signal output of amplifier 26b is applied through a resistor 66 to the gate terminal of a silicon controlled rectifier 68 which directly operates a deluge valve 70 or the like as discussed above with respect to the deluge valve 46 or other suitable electrically actuated component for activating the protective system. A positive high voltage potential is applied to a supply terminal 72 to which the valve 70 is connected.

The quenching circuit 16 is illustrated in detail in FIG. 5; the leads 12, 14 and 17 in FIG. 1 are referenced in FIG. 5 to show the manner in which the quenching circuit 16 is interconnected with the photodiode 11 and the input to the one shot 18. A positive high voltage potential for operating the photo-diode 11 is applied to power terminal 74; the terminal 76 is the common return for the high voltage supply and the low voltage (+V) utilized to operate the transistor configuration. The photo-diode 11 may comprise an ultraviolet sensitive gas discharge tube such as, for example, a type 129464F manufactured by Honeywell Incorporated.

A pair of series connected Zener diodes 78 are connected in series with a third Zener diode 80, the three diodes being connected across power leads 82 and 84 extending from terminals 74 and 76 to regulate the high voltage supply. Normally, the rating of the Zener diode 80 would be substantially less than either of the diodes 78 for a purpose to be discussed hereinafter. The positive high voltage supply lead 82 is connected to lead 14 by a. variable resistor 86, the return lead 84 being connected to lead 12 by a capacitor 88.

A resistor interconnects lead 12 and the base of a normally nonconducting, NPN transistor 92. The transistor 92 has its emitter output connected to the base of a second normally nonconducting, NPN transistor 94, the collector of transistor 94 being connected to a junction point 96 to which the cathode of Zener diode 80 is also connected. A resistor 98 connects junction point 96 with the base of a normally conducting NPN transistor 100, the collector of the transistor 100 being connected to the lead 17 extending to the input of one shot 18.

OPERATION Referring first to the embodiment of FIG. 1, the sensing diodes 11 of the two pulse producing circuitries 10 and 10a are disposed in a region, such as a warehouse or laboratory area, desired to be protected from fire and explosion. Depending upon the volume to be covered and the physical layout of the region upon protection, it may be desired to employ a number of pairs of sensors associated with various subregions of the region under protection in order to provide complete coverage and insure nearly instantaneous detection of the presence of a flame. Being an ultraviolet sensor, the photo-diodes 11 do not respond to infrared or other lower frequency radiation; however, the diodes are sensitive to stray radiation such as cosmic rays or bombardment by atomic particles. Also, such natural phenomena as reflections of the sun may also be sensed and present the possibility of inadvertent activation of the protective system. For these reasons, therefore, the two sensors of the dual channel arrangement of FIG. 1 are purposely spaced apart to minimize simultaneous exposure of both sensors to bursts of random radiation. This spacing may only be a matter of a few inches and the sensors may be essentially disposed side-by-side, or the spacing may be greater, depending upon the physical layout of the region to be monitored.

Regardless of the nature of the sensed energy, the gas discharge photo-diode 11 ionizes when sensing occurs and the resultant breakdown produces a short duration spike pulse as illustrated at 102. If the radiation persists, a train of the spikes 102 is produced, the spacing between adjacent spike pulses 102 being inversely proportional to the intensity of the sensed radiation. Therefore, the repetition rate of the spike pulses 102 is a measure of the intensity of the sensed radiation and is advantageously employed as discussed below.

The function of the quenching circuit 16 associated with each photo-diode 11 is to limit the rate of ionization breakdown to thereby prevent multiple firing of the sensing tube by random radiation. Referring to FIG. 5, when breakdown occurs the potential standing on lead 12 will be momentarily raised to a higher positive potential to charge the capacitor 88 and gate the transistor 92, causing the latter to momentarily assume its conductive state. The transistor 92 is held on for a length of time determined by the charge developed on capacitor 88 and the value of the resistor 90. When transistor 92 is turned on, the transistor 94 is also rendered conductive to, in turn, short across Zener diode 80 and momentarily lower the potential at junction point 96 to substantially that of the return supply lead 84. This lowers the voltage across the cathode and anode of the sensing tube 11 to prevent the same from firing again until full potential is reestablished. The ratings of the Zener diodes 78 and 80 are selected such that, with diode 80 effectively removed from the circuit, the potential delivered to the tube 11 is below the minimum firing potential thereof. At the time that transistor 94 goes into conduction, the lowering of the potential at junction point 96 turns transistor 100 off to raise the potential at its collector and deliver a positive pulse illustrated at 104 along lead 17 to the one shot 18.

The one shot 18 inverts, shapes and lengthens the positive input pulses 104 to provide a train of square wave impulses illustrated at 106. The amplifier 26 serves as a detector to determine if the intensity of the sensed radiation is equal toor above the maximum expected background level of the radiation in the region under protection. The sensitivity of the amplifier 26 is set by the variable resistor 22, it being understood that an increased resistance presented to the negative impulses 106 reduces the input current at the inverting input of amplifier 26, the inverting input being held at a positive po tential in the absence of the negative input signal.

The detection function accomplished by the amplifier 26 is illustrated in FIG. 4. The input impulses 106 are plotted on the first graph where it is illustrated that each impulse 106 drives the inverting input of the amplifier 26 negative to cause the output voltage of amplifier 26 (plotted on the second graph) to rise. The integrating action is seen by the stair-stepped wave 108, each step reaching a maximum at the termination of a corresponding impulse 106, then falling slightly between input impulses 106, and rising again on the subsequent impulse. In the example of FIG. 4, the output wave 108 reaches the zero crossing during the third impulse 106, whereupon the amplifier goes into positive saturation and temporarily latches. The duration of the latch is controlled by selection of the values of capacitor 36 and resistor 38. Therefore, it may be appreciated that the amplifier 26 will excite one input of the AND gate 42 if the repetition rate of the impulses 106 at its input over a predetermined time period is such as to permit integration to the zero crossing point of the amplifier output.

When the output of amplifier 26 goes positive, the switching transistor 50 is rendered conductive and the lamp 52 lights to warn an observer that the radiation intensity has reached the maximum expected background level. In applications where the region under protection is subject to the hazard of a very slowly developing fire condition, the warning light 52 would signal that the region should be checked for the possibility of such a condition. On the other hand, the energization of the warning light 52 could also indicate a failure of a component in the apparatus or indicate that the apparatus is in need of adjustment. It should be understood that a false warning, insofar as a danger is concerned, is preferred to inadvertent activation of the protective system with resultant unnecessary discharge of a fire suppressant.

The second sensing channel operates in identically the same manner as discussed above, except that the amplifier 26a is set to respond with a positive output command signal when the integration of its input impulses is indicative'of an excessive radiation condition. This excessive condition is set from a known ultraviolet source at a fixed distance from the sensing tube of the channel. Thus, with like parameters elsewhere, the resistance of the variable resistor 22;: would be higher than the resistance of resistor 22 to render the amplifier 26a less sensitive to the input impulses. The integation constant for amplifier 26a would, of course, be set to preclude the production of a command signal at the amplifier output unless a radiation intensity is sensed that is clearly caused by the existence of a flame. Therefore, an output from both of the amplifiers 26 and 26a is required before SCR 44 is fired to activate the protective system.

Through the use of the dual channel arrangement, the

apparatus may be permitted to respond rapidly to a flame condition with assurance that the condition being sensed is an actual flame and not stray radiation. This is a result of the spacing of the two sensing tubes 11 which minimizes simultanesous exposure thereof to stray radiation, plus the employment of the integrators in the detection of appropriate intensity levels.

In FIG. 2, operation is the same as above except that the advantages of dual sensing channels are not realized. However, the higher sensitivity of the amplifier 26 will operate the warning light 52 and thus provides a measure of protection against inadvertent activation of the extinguishing system.

In the embodiment of FIG. 3, only a single integrator amplifier 26b is employed as a detector, but the impulses 106 from the two one shots 18 and 18a are fed to the AND gate 58 rather than directly to the integrator. Thus, the advantages of dual channel sensing are realized since the one shot outputs must be in time coincidence before an input signal is delivered to the amplifier 26b. In the case of stray radiation, the probability of the one shot outputs being coincident is remote. Furthermore, the amplifier 26b is set at the same integration constant as amplifier 26a discussed above, so that the command signal from its output is produced only when the repetition rate of the input signals to the amplifier is indicative of a dangerous radiation condition. The embodiment of FIG. 3 is illustrated as employing a reset switch 64 since permanent latch-up of the amplifier output occurs when it goes positive and gates the SCR 68.

It has been found that the instant invention can readily respond in 15 to 20 milliseconds and, utilizing a detonatable deluge valve, approximately another 5 to 10 milliseconds is consumed in the delivery of the suppressant into the region under protection. Therefore, a maximum total time from flame initiation to suppressant delivery of 30 milliseconds is readily realizable. This extremely fast action requires a suppressant such as Freon in order to take maximum advantage of the speed of the system.

For example, a methane atmosphere with an optimum mixture for explosion requires approximately 55 milliseconds from the time of ignition to the time when maximum expansion of the gases commences and the explosion irreversibly commences. Thus, a protective system must quench the flame within the 55 milliseconds burning period before the gases commence expansion at the explosion rate. Therefore, with proper suppressant selection, the apparatus of the instant invention has a response time well within the necessary requirement for a practical explosion protection system.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. Apparatus for monitoring radiation conditions in a region and for producing an electrical output signal in response to an excessive radiation condition, said apparatus comprising:

first and second radiation responsive input means having first and second radiation sensors respectively disposed to sense radiation of a predetermined character in said region impinging thereupon and spaced apart to minimize simultaneous exposure of both sensors to bursts of random radiation,

each of said sensors being a photo diode of the ionization breakdown type,

each input means being responsive to the radiation impinging on the sensor thereof for providing time spaced electrical impulses having a repetition rate dependent upon the intensity of the sensed radiation, and having quenching means coupled with its sensor for limiting the rate of ionization breakdown thereof to prevent multiple firing of the sensor by said random radiation; and

output means coupled with said first and second input means for delivering said output signal when both 7 of the sensors are exposed to radiation of said character and the repetition rates of the impulses from respective first and second input means correspond to predetermined radiation intensities greater than the normal background level.

ing a second command signal when the repetition rate thereof over a preselected time duration corresponds to a radiation intensity indicative of said excessive radiation condition, and means coupled with said detectors and responsive to said command 2. Apparatus for monitoring radiation conditions in signals therefrom for effecting said delivery of the a region and for producing an electrical output signal in output signal when both the first and the second comresponse to an excessive radiation condition, said appamand signals occur in time coincidence. ratus comprising: 5. Apparatus as claimed in claim 4,

first and second radiation responsive input means 10 and a warning device coupled with said first detector having first and second radiation sensors respectively for activation in response to said first command disposed to sense radiation of a predetermined charsignal. acter in said region impinging thereupon and spaced 6. Apparatus for monitoring radiation conditions in a apart to minimize simultaneous exposure of both region and for producing an electrical output signal in sensors to bursts of random radiation, response to an excessive radiation condition, said apparatus each input means being responsive to the radiation comprising:

impinging on the sensor thereof for providing time first and second radiation responsive input means having spaced electrical impulses having a repetition rate first and second radiation sensors respectively disdependent upon the intensity of the sensed radiation; posed to sense radiation of a predetermined character and in said region impinging thereupon and spaced apart output means coupled with said first and second input to minimize simultaneous exposure of both sensors means for delivering said output signal when both to bursts of random radiation, of the sensors are exposed to radiation of said each input means being responsive to the radiation imcharacter and the repetition rates of the impulses pinging on the sensor thereof for providing time from respective first and second input means corre- 5 spaced electrical impulses having a repetition rate despond to predetermined radiation intensities greater pendent upon the intensity of the sensed radiation; than the normal background level. and

said output means including a first detector responsive output means coupled with said first and second input to the impulses from said first input means for demeans for delivering said output signal when both of livering a first command signal when the repetition the sensors are exposed to radiation of said characrate thereof corresponds to the respective predeterter and the repetition rates of the impulses from mined radiation intensity, a second detector responrespective first and second input means correspond sive to the impulses from said second input means to predetermined radiation intensities greater than for delivering a second command signal when the the normal background level,

repetition rate thereof corresponds to the respective said output means effecting delivery of said output signal predetermined radiation intensity, and means when the impulses from said first and second input coupled with said detectors and responsive to sai means occur in time coincidence and at a repetition Command S gnals therefrom for effecting said derate corresponding to a radiation intensity indicative livery of the output signal when both the first and of said excessive radiation condition,

the second command signals occur in time coinci- 7. Apparatus as claimed in claim 6,

dence. said output means including an AND gate having a pair 3. Apparatus as claimed in claim 2, of inputs for receiving said impulses from respective each of said detectors including means for integrating first and second input means, and means coupled with the impulses from the corresponding input means. the output of the AND gate for detecting the repeti- 4. Apparatus for monitoring radiation conditions in a tion rate of gate pulses therefrom to effect said deregion and for producing an electrical output signal in livery of the output signal when the detected repetiresponse to an excessive radiation condition, said appation rate is indicative of said excessive radiation ratus comprising: iti

first and second radiation responsive input means 8. Apparatus as claimed in claim 6,

having first and second radiation sensors respectively said output means including an AND gate having a disposed to sense radiation of a predetermined charpair of inputs for receiving said impulses from reacter in said region impinging thereupon and spaced spective first and second input means, and means apart to minimize simultaneous exposure of both coupled with the output of the AND gate for insensors to bursts of random radiation, tegrating gate pulses therefrom and effecting said each input means being responsive to the radiation delivery of the output signal when the repetition rate impinging on the sensor thereof for providing time of the gate pulses over a predetermined time period spaced electrical impulses having a repetition rate is indicative of said excessive radiation condition. dependent p the intensity of the sensed radiation; 9. Electric apparatus for monitoring radiation condiand tions and for producing an output signal in response to an Output means coupled Wlth Sald first Second Input 0 excessive radiation condition, said apparatus comprising: mea r delivering Said p t sfghal f both means for sensing radiation of a predetermined charof the sensors are exposed to radiation of said character and f providing i Spaced electrical i acter and the repetition rates of the impulses from pulses having a repetition rate dependent upon the respective first and second input means correspond intensity of the sensed radiation; to predetermined radiation intensities greater than a fi detector coupled with said sensing means and the normal background level, responsive to said impulses for integrating the latter said output means including a first detector responsive and delivering a first command signal when the repefl t0 the impulses from, Said t ihPut meahs for lnte' tion rate of the impulses over a predetermined time grating the last hlehtlohed lthphlses "fh dehvenhg period corresponds to a radiation intensity equal to first Command slgnal when the fepetltloll rate there the maximum expected background level of the radiaof over a predetermined time period corresponds to i a radiation intensity equal to the maXimum expected a warning device coupled with said first detector for background level, a Second detector responsive to activation in response to said first command signal; the impulses from said second input means for a second detector coupled with said sensing means and integrating the last mentioned impulses and deliverresponsive to said impulses for integrating the latter and delivering a second command signal when the repetition rate of the impulses over a preselected time duration corresponds to a predetermined radiation intensity indicative of said excessive radiation conditon; and

therefrom for effecting actuation of said control means when both the first and the second command signals occur in time coincidence.

14. Apparatus as claimed in claim 12,

the intensity dependent signal of each input means means coupled with said detectors and respinsive toincluding time spaced electrical impulses having a said command signals therefrom for delivering said repetition rate presenting said characteristic thereof, output signal when both the first and the second said output means efiecting actuation of said control command signals occur in time coincidence. means when the implses from said first and second 10. Apparatus as claimed in claim 9, input means occur in time coincident and at a repesaid sensing means including a pair of independent radiation sensors and means responsive to each of said sensors respectively for delivering a train of said tition rate corresponding to a radiation intensity indicative of said excessive radiation condition. 15. Apparatus for monitoring radiation conditions and for actuating fire or explosion protection system in response to an excessive radiation condition, said apparatus comprising:

impulses exclusively to a corresponding detector. 11. Apparatus as claimed in claim 9, said sensing means including a radiation sensor and means responsive to said sensor for delivering said impulses to both of said detectors concurrently. 12. Apparatus for monitoring radiation conditions in means for sensing radiation of a fire or explosion indicating character and for providing an electrical signal having a characteristic dependent upon the intensity of the sensed radiation; first detector coupled with said sensing means and responsive to said intensity dependent signal for first and second radiation responsive input means having first and second radiation sensors respectively delivering a first command signal when said characteristic corresponds to a radiation intensity equal disposed to sense radiation of a fire or explosion to the maximum expected background level of the indicating character in said region impinging thereradiation; upon and spaced apart to minimize simultaneous a warning device coupled with said first detector for exposure of both sensors to bursts of random activation in response to said first command signal; radiation. a second detector coupled with said sensing means each input means being responsive to the radiation imand responsive to said intensity dependent signal for pinging on the sensor thereof for providing an delivering a second command signal when said charelectrical signal having a characteristic dependent acteristic corresponds to a predetermined radiation upon the intensity of the sensed radiation; intensity indicative of said excessive radiation electrically responsive control means for initiating condition;

operation of said system; and electrically responsive control means for initiating output means coupled with said first and second input operation of said system; and

means and said control means for exciting the latter means coupled with said detectors, responsive to said to etfect operation of said system when both of the command signals therefrom, and coupled with said sensors are exposed to radiation of said character control means for exciting the latter to effect operaand the characteristics of the signals from respection of said system when both the first and the tive first and second input means correspond to presecond command signals occur in time coincidence. determined radiation intensities greater than the normal background level. References Cit d 13. Apparatus as claimed in claim 12, UNITED STATES PATENTS said output means including a first detector responsive to the intensity dependent signal from said first in- 3,130,310 4/1964 Biberman et al.

put means for delivering a first command signal 3,161,774 12/1964 Pinckaers.

when the characteristic thereof corresponds to the 3,274,580 9/1966 Thomson 340-228 respective predetermined radiation intensity, a sec- 3,307,696 3/ 1967 g ond detector responsive to the intensity dependent signal from said second input means for delivering a second command signal when the characteristic thereof corresponds to the respective predetermined radiation intensity, and means coupled with said detectors and responsive to said command signals ARCHIE R. BORCHELT, Primary Examiner US. Cl. X.R. 

